Olefin metathesis reactions allow us to break bonds between two olefins and rearrange their substituents before reforming those bonds. Olefin metathesis is most prominent in the industry, where it is utilized to make precursors for products such as detergents, polypropylene plastic, and medications. The majority of the currently used molybdenum and tungsten alkylidenes are formed by two methods: alpha-hydrogen abstraction of metal polyalkyls complexes and protonation of alkylidynes. Recently we discovered a method of forming alkylidenes <i>in situ</i> by reacting molybdenum benzylidyne complexes with olefins. This is the first reported instance of a molybdenum alkylidyne complex performing olefin metathesis. Presumably, the reaction occurs through an alkylidene intermediate. Noteworthy, NMR shows the alkylidyne complex regenerates after each catalytic cycle. 13C labeling studies showed the benzylidyne ligand stayed attached to the complex throughout the catalysis; using this information, a mechanism for the reaction was proposed. Since the benzylidyne ligand remains bound to the complex, it can be altered and used as another parameter to adjust the complex reactivity towards olefin metathesis. This contrasts with a metal carbene catalyst whose carbene ligand does not stay attached to the catalysts throughout the catalytic cycle. We also found that electron-donating properties of the benzylidyne group have a significant impact on the metathesis activity. Thus, the change of methoxy group on the benzylidyne ligand for electron-withdrawing NO2 and CF3 groups increases the conversion of the ring-closing metathesis for diallyl N-tosylamide from 13% to over 99%.

Molybdenum benzylidyne complexes for olefin metathesis reactions

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.